Coastal Geology
Borrow Area Design
CPE collects extensive geophysical and geotechnical data during a sediment search investigation. Information related to sediment quality is based on both vibracores and seismic data. Vibracores are used to determine the quality of the sediment and to ground truth seismic data. The seismic data is used to determine the sediment thickness. This process provides a three dimensional seismic mapping of the potential sand resource. Images of the seafloor produced from the sidescan sonar data, are used in conjunction with magnetometer data in order to identify avoidance areas such as existing infrastructure, modern debris or potentially culturally significant resources. Remotely sensed data is also be used to identify natural resources such as offshore reefs, nearshore hardbottom, or seagrasses. The bathymetric data collected during the geophysical surveys is used to determine the elevation of the seafloor and the elevation of beach compatible sediment.
Once all of this data has been collected and assessed, a borrow area is developed. Design cuts are based a variety of factors including (but not limited to) deposit geometry, sediment quality, dredgability (i.e. minimum water depths, minimum swath width and length), volume requirements, potential nearshore impacts, and relative cost of dredging the material. Any areas identified for avoidance (i.e. cultural resources, infrastructure, hardbottom, etc.) are incorporated into the borrow area design.
Often dredge plans are required to provide the most efficient utilization of the entire volume of borrow area sediment. A dredge plan specifies the sequence of excavation areas within the borrow area such that the remaining material after each nourishment event will reside within the borrow area cut where it can be efficiently and economically excavated during subsequent events.
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